Knee Gel Injections: Common Side Effects, Rare Risks, and When to Seek Help

What are the side effects of gel injections in the knees?

Gel injections, also known as viscosupplementation, are generally well-tolerated, but can cause localized reactions such as pain, swelling, and warmth at the injection site, with rare but more serious risks including infection or severe inflammatory responses.

Gel injections, medically termed viscosupplementation, involve injecting a hyaluronic acid (HA) solution into the knee joint. This procedure is primarily used to treat osteoarthritis, where the natural synovial fluid, which contains HA, has thinned and lost its lubricating and shock-absorbing properties. The injected HA aims to supplement the joint's natural fluid, potentially reducing pain and improving mobility. While often beneficial, like any medical procedure, it carries potential side effects.

Common Local Side Effects

The most frequently reported side effects are localized reactions at or around the injection site. These are typically mild and transient, resolving within a few days. They include:

• Pain or Discomfort at the Injection Site: This is the most common side effect, often described as a dull ache or soreness that subsides quickly.
• Swelling: Mild to moderate swelling around the knee joint is common as the body reacts to the injected substance.
• Warmth: A sensation of warmth in the knee, indicating increased blood flow to the area.
• Redness: Slight redness or erythema at the injection site.
• Bruising: Minor bruising can occur if a small blood vessel is nicked during the injection.
• Joint Stiffness: A temporary increase in stiffness in the knee, especially immediately after the injection.

These common side effects are typically managed with rest, ice application, and over-the-counter pain relievers such as acetaminophen or NSAIDs.

Less Common and More Serious Side Effects

While rare, more significant side effects can occur. Understanding these is crucial for both patients and practitioners.

• Acute Pseudoseptic Reaction (Sterile Inflammation): This is an uncommon but notable side effect where the joint develops a severe inflammatory response, mimicking a joint infection (septic arthritis) but without actual bacterial involvement. Symptoms include significant pain, swelling, warmth, and tenderness. This reaction is thought to be an immune response to the hyaluronic acid itself. It usually resolves spontaneously or with anti-inflammatory medication, but it is critical to differentiate it from true infection.
• Infection (Septic Arthritis): This is a very rare but serious complication. Any joint injection carries a small risk of introducing bacteria into the joint space, leading to a severe infection. Symptoms include intense and worsening joint pain, severe swelling, redness, warmth, fever, chills, and general malaise. Septic arthritis is a medical emergency requiring immediate antibiotic treatment and potentially surgical drainage to prevent permanent joint damage. Strict aseptic technique during the injection is paramount to minimize this risk.
• Allergic Reactions: Although uncommon, some individuals may have an allergic reaction to the components of the gel injection. Symptoms can range from mild skin rashes (hives, itching) to more severe systemic reactions like difficulty breathing (anaphylaxis), though the latter is extremely rare. Patients with known allergies to bird products (as some HA is derived from rooster combs) or other components should inform their physician.
• Bleeding: While minor bruising is common, significant intra-articular bleeding (hemarthrosis) is rare but can occur, especially in individuals on blood thinners or with bleeding disorders.
• Nerve or Tissue Damage: With proper technique and imaging guidance (if used), damage to surrounding nerves, ligaments, or cartilage is exceedingly rare.

Factors Influencing Side Effects

Several factors can influence the likelihood or severity of side effects:

• Patient Health Status: Individuals with compromised immune systems, active skin infections near the injection site, or certain bleeding disorders may be at higher risk for complications.
• Injection Technique: The skill and experience of the injecting physician, along with strict adherence to sterile procedures, significantly impact the safety of the procedure. Accurate needle placement is also crucial.
• Type of Hyaluronic Acid Product: Different HA products vary in molecular weight, cross-linking, and source, which might subtly influence the body's reaction, though clinical differences in side effect profiles are generally minor across approved products.

When to Seek Medical Attention

While most post-injection discomfort is mild and resolves quickly, it's crucial to be aware of warning signs that warrant immediate medical evaluation. Contact your healthcare provider immediately if you experience:

• Severe or rapidly worsening pain in the injected knee.
• Significant and persistent swelling, redness, or warmth that is not improving.
• Fever or chills.
• Pus or drainage from the injection site.
• Signs of a systemic allergic reaction, such as widespread rash, itching, hives, difficulty breathing, or dizziness.

Understanding Benefits vs. Risks

For many individuals with knee osteoarthritis, viscosupplementation offers a non-surgical option to reduce pain and improve function when other conservative treatments (physical therapy, oral medications, steroid injections) have not provided sufficient relief. While side effects are a possibility, the vast majority are mild and temporary. Serious complications like infection are exceedingly rare. The decision to undergo gel injections should always involve a thorough discussion with a qualified healthcare professional, weighing the potential benefits against the individual's specific risk factors and health profile.